Cobalt-vanadium-iron alloy

ABSTRACT

DESCRIBED HEREIN IS AN IMPROVED ALLOY POSSESSING AN OUTSTANDING COMBINATION OF STRENGHT AND ELECTRICAL PROPERTIES WHICH CONSISTS ESSENTIALLY OF COBALT, VANADIUM, MOLYBDENUM AND IRON AND IN WHICH THE MOLYBDENUM IS LIMITED TO 0.25 TO 1% WITH A COMBINED VANADIUM PLUS MOLYBDENUM CONTENT OF 1.5 TO 2.5%.

United States Patent Oflice 3-,704,1 l8 Patented Nov. 28, 1972 3,704,118 COBALT-VANADIUM-IRON ALLOY Carl P. Stroble, Natrona Heights, Pa., assignor to Allegheny Ludlum Industries, Inc., Pittsburgh, Pa.

N Drawing. Continuation-impart of application Ser. No. 47,127, June 17, 1970. This application Dec. 27, 1971, Ser. No. 212,702

Int. Cl. C22c 19/00 US. Cl. 75-170 4 Claims ABSTRACT OF THE DISCLOSURE Described herein is an improved alloy possessing an outstanding combination of strength and electrical proper ties which consists essentially of cobalt, vanadium, molybdenum and iron and in which the molybdenum is limited to 0.25 to 1% with a combined vanadium plus molybdenum content of 1.5 to 2.5%.

This application is a continuation-in-part of application Ser. No. 47,127 filed June 17, 1970, now abandoned.

This invention relates to an improved alloy combining high strength and good magnetic properties rendering it suitable for electrical applications. As a result of the increasingly high operating speeds of from 8,000 to 20,000 r.p.m. to which aircraft generators and similar components are subjected, mechanical strength requirements of alloys used in the electrical applications for these purposes, such as the construction of generator rotors, have been substantially increased. Most commonly, an alloy is used which possesses excellent magnetic properties and which contains a combination of cobalt, iron and vanadium. Such an alloy is known commercially as Vanadium Permendur and nominally contains 47.5 to 50.5% cobalt, 1.7 to 2.1% vanadium and the balance essentially iron.

Although specifications of strengths and electrical properties for these alloys differ in different applications, some requirements have been that the alloy possess a minimum 0.2% offset yield strength of 70,000 p.s.i. and a minimum tensile elongation of 5% with relatively little deterioration in magnetic properties. Presently available Vanadium Permendur alloy develops a yield strength of about 55,000 p.s.i. after annealing, e.g., for four hours at 1385 F. The present invention provides an improved, modified Vanadium Permendur which possesses increased yield strength without undue sacrifice of magnetic properties. Strip and laminations made of the alloy in accordance with the invention are essentially insensitive to normal variations in annealing conditions, temperature and time at temperature and thus provide more latitude in processing to achieve products with improved properties. In accordance with the invention, it has been discovered that the addition of controlled quantities of molybdenum with critical and controlled combination of total vanadium plus molybdenum content can result in an alloy of improved mechanical properties and satisfactory magnetic properties as Well. Alloys in accordance with the invention consist essentially of 47.5 to 50.5% cobalt, 1.25 to 2.1% vanadium, 0.25 to 1% molybdenum, the total vanadium plus molybdenum content being within the range of 1.5 to 2.5%, preferably about 2%, carbon preferably up to 0.1%, and the balance essentially iron.

It has been discovered that molybdenum acts to decrease the recrystallized grain size developed during the annealing of cold rolled Vanadium Permendur strip or laminations. The observed grain size refinement is associated with an increase in yield strength over that produced in a normal alloy by the same heat treatment. Ductility, as measured by percent elongation and tensile tests, is also found to be greater in molybdenum-bearing alloys than in the non-molybdenum-containing compositions.

Although some grain growth occurs in molybdenumcontaining alloys during prolonged annealing or upon annealing at higher temperatures, grain growth rates are lower in the molybdenum alloy than in the alloy devoid of molybdenum. In a co-pending application, Ser. No. 47,126, filed June 17, 1970, there is disclosed a modified Vanadium Permendur containing controlled quantities of carbon. The carbon is described as restricting grain growth tendencies. The molybdenum addition in accordance with the present invention, can be made to alloys of controlled carbon content such as disclosed in the aforementioned co-pending application with additional improvement in properties.

A particular advantage of the present invention is that high yield strength can be obtained in fully recrystallized alloys with molybdenum, whereas in alloys without molybdenum comparable strengths may be obtained only in the partially recrystallized or barely recrystallized condition. This characteristic greatly increases the range of annealing conditions, i.e., time and temperature, which are suitable for the development of high strength in the molybdenum-containing alloys of the invention. Grain growth inhibition resulting from the addition of carbon further reduces sensitivity to annealing conditions. Although some decrease in magnetic properties may be observed in molybdenum-containing alloys, controlled quantities of molybdenum will still result in alloys of greater strength but satisfactory magnetic properties. In this connection it is noted that it is necessary to restrict the molybdenum plus vanadium content to within the range of 1.5 to 2.5% This restriction is necessary because the grain growthrestricting properties of the molybdenum-modified alloy are presently believed to derive from the formation of some austenite. Alloys containing less than 1.5% combined molybdenum plus vanadium content, result in inadequate austenite formation and, therefore, little or no strengthening. However, at quantities of vanadium plus molybdenum greater than 2.5 there is excessive austenite formed and there results a disproportionately harmful affect on magnetic properties.

The advantage of modifying Vanadium Permendur by the addition of molybdenum, is apparent from an inspection of the data reported in the following tables. The properties in Table -II are of composition disclosed in Table I. The samples of vacuum induction melted heats contain nominally from 0.25 to 0.75% molybdenum by weight. Compositions were adjusted so that in each instance the total concentration of molybdenum plus vanadium was nominally about 2% by weight. Tensile tests and magnetic tests were performed on 1" x 1 /2" rings of 10 mil thick samples annealed as shown in the tables.

TABLE I Percent of- TABLE II Tensile properties, Permeability, (1.0.

percent Core loss Anneal H at B at .2 yield Elon' 400 Hz., 400 Hz., 2,400 Hz., 2,400 Hz.,

Heat F. Hours strength gation 20 kb. 22 kb. H H H H 200 H 15 kb. 20 kb. 10 kb. 15 kb.

RV4097- 1, 350 4 62,350 7. 8 12 44 19, 500 21, 020 2, 22, 650 23, 000 28. 5 53. 4 142 341 RV4097- 1, 400 2 67, 560 9. 0 8. 98 33 20, 200 370 22, 400 22, 840 23, 090 23. 5 38. 6 121 293 RV409 1, 450 4 55, 550 10. 0 9. 02 34 20, 190 21, 325 22, 425 22, 820 23, 26. 4 46. 9 131 324 RV4097- 1, 550 4 48, 550 9. 0 8. 88 30. 4 20, 200 21, 420 22, 480 22, 860 23, 130 16. 0 26. 1 105 247 RV4098. 1, 350 4 75, 650 9. 8 11. 3 42 19, 750 21, 070 22, 190 22, 670 23, 050 30. 9 52. 6 376 RV4098. 400 2 83,350 7. 5 12 43 19, 550 20, 970 22, 130 22, 670 030 32. 8 57. 8 173 399 RV4098- 1, 450 4 71, 750 9. 5 9. 32 35 20, 135 21, 320 22, 330 22, 760 23, 075 31. 9 49. 3 164 389 RV409 1, 550 4 53, 950 10 13. 7 40 19, 200 20, 770 22, 24.) 22, 820 23, 200 10. 5 31. 6 126 291 RV4105-.. 1,350 4 77, 700 9. 5 11. 4 40. 2 19, 750 07 22, 190 22, 720 23, 100 33. 1 58. 8 167 397 RV4105- 1, 400 2 83, 045 9. 5 11. 5 41 19, 650 21, 020 22, 22, 720 23, 090 35. 9 67. 0 180 425 RV4105- 1, 450 4 70, 200 7. 8 9. 08 35 20, 21, 320 22, 330 22, 810 23, 120 23. 9 40. 6 127 313 RV4105. 1, 550 4 61, 250 7. 8 13 43 19, 400 20, 880 22, 22, 780 23, 150 23. 8 42. 6 138 331 RV4106-.- 1,350 4 550 8. 5 11. 4 40 19, 700 21, 080 22, 190 22, 730 23, 120 37. 2 71. 2 101 451 RV4106 1, 400 2 87, 190 7. 8 14. 2 56 19, 100 20, 670 21, 920 22, 480 23, 000 41. 7 77. 1 216 474 RV4106. 1, 450 4 75, 400 7. 5 9. 4 36 20, 040 21, 275 22, 330 22, 755 23, 050 26. 7 47. 4 144 363 RV4106- 1, 550 4 68, 800 9. 0 12. 4 40 19, 500 20, 930 22, 250 22, 790 23, 190 27. 8 51. 6 161 395 4 46, 550 8. 0 8. 28 40 20,300 21, 330 22, 140 22, 480 22, 710 14. 4 23. 2 93. 1 247 It can be seen by comparm g the properties of heat 1. An improved alloy consisting essentially of 47.5 to

82228, substantially devoid of molybdenum, with the properties of the other heats, that the mechanical properties are substantially improved by the addition of controlled amounts of molybdenum. Similarly, the somewhat decreasing magnetic properties are also illustrated to be related to increasing molybdenum concentration. However, as pointed out previously, contents of molybdenum greater than 1% and/ or amounts of vanadium plus molybdenum greater than 2.5% result in disproportionately greater decrease in magnetic properties presently believed to be due primarily to excessive austenite formation. The composition of heat 82228 is typical of present day commercial alloys of Vanadium Permendur.

The effects of additional annealing cycles on the properties of the alloys disclosed in the tables, illustrate the greater latitude in permissible annealing conditions for alloys in accordance with the invention. This characteristic can be important from the practical point of view in permitting greater variation in processing conditions without undue deleterious effect on properties.

It is apparent from the foregoing that various changes and modifications may be made without departing from the invention. Accordingly, the scope of the invention should be limited only by the appended claims, wherein what is claimed is:

50.5% cobalt, 1.25 to 2.1% vanadium, 0.25 to 1% molybdenum, the total vanadium plus molybdenum content being within the range of 1.5 to 2.5% and the balance essentially iron.

2. An improved alloy according to claim 1 wherein the total vanadium plus molybdenum content is about 2%.

3. A cold worked and subsequently fully recrystallized, alloy consisting essentially of 47.5 to 50.5% cobalt, 1.25 to 2.1% vanadium, 0.25 to 1% molybdenum, the total vanadium plus molybdenum content being within the range of 1.5 to 2.5%, and the balance essentially iron; said alloy having a minimum yield strength of 70,000 p.s.i.

4. An alloy according to claim 3 wherein the total vanadium plus molybdenum content is about 2%.-

References Cited UNITED STATES PATENTS 1,862,559 6/1932 White et a1. 7517O RICHARD O. DEAN, Primary Examiner US. Cl. X.R. 

